Syrian President Bashar Assad has said his government will implement a deal reached with the United States and Russia to dispose of Syria's chemical weapons.

But Assad said destroying Syria's chemical weapons would cost $1 billion and would take about a year.

Assad also told Fox News on September 18 that a UN report that found "clear and convincing evidence" of a sarin nerve gas attack in Syria last month was "unrealistic."

He again denied his forces were behind the August 21 attack in the suburbs of Damascus that that the United States says killed some 1,400 people.

"The whole story doesn't even hold together," he said. "It's not realistic. So, no, we didn't, in one word. We didn't use any chemical weapons in Ghouta because if you want to use it, you would harm your troops, you would have harmed the tens of thousands of civilians living in Damascus."

Earlier, Russian Foreign Minister Sergei Lavrov said Moscow had obtained evidence indicating the rebels were behind the August attack in Ghouta.

He told reporters that Russian officials would soon present this evidence to the UN Security Council.

"We have enough evidence that information about the use of chemical weapons reflects the fact that the opposition regularly resorts to provocation in order to bring in strikes, intervention against Syria," Lavrov said. "There is a lot of data, it is easily accessible on Internet. This data is also in the report prepared by our experts on the events connected to the use of chemical weapons in the Aleppo area in March this year."

Also on September 18, Russia criticized the UN report on the August 21 poison gas attack.

Russian Deputy Foreign Minister Sergei Ryabkov said the report released on September 16 was "one-sided."

Reacting to that criticism, UN spokesman Martin Nesirsky said the findings of UN chemical weapons experts that rockets loaded with sarin gas were used in the August 21 attack "are indisputable."

Meanwhile, envoys from the five permanent members of the UN Security Council met for more consultations on September 18 to discuss a draft resolution prepared by Britain, France, and the United States.

Russia again said the draft should leave out any threat of force if Syria fails to dispose of its chemical weapons.

Inside Syria, a rebel group allegedly linked to Al-Qaeda was reported to have overrun a Syrian town near the border with Turkey on September 18.

Opposition activists said fighters from the Islamic State of Iraq and the Levant stormed the town of Azaz and killed five Free Syrian Army members.